In JP 2005-308178 A, there is discussed a damping force adjustable hydraulic shock absorber used as a vehicle suspension. This hydraulic shock absorber includes a cylinder, a piston that partitions the inside of the cylinder into an expansion-side chamber and a contraction-side chamber, a piston rod movably inserted into the cylinder with one end being connected to the piston, a passage provided in the piston to cause the expansion-side chamber and the contraction-side chamber to communicate with each other, a valve seat provided in the middle of the passage, a spool seated on or unseated from the valve seat to open or close the passage, an expansion-side pilot chamber that applies a pressure from the expansion-side chamber to a part of the back face of the spool, a contracting-side pilot chamber that applies a pressure from the contraction-side chamber to the other part of the back face of the spool, and solenoid pressure control valves provided in the middle of the expansion-side pilot passage and the contraction-side pilot passage to control pressures of the expansion-side pilot chamber and the contracting-side pilot chamber.
In this hydraulic shock absorber, damping forces of the expanding and contracting motions are controlled by controlling the pressure of the back-pressure chamber by using the solenoid pressure control valve. Specifically, the hydraulic shock absorber includes a first poppet valve provided in the middle of the expansion-side pilot passage to operate during an expanding motion, and a tubular second poppet valve arranged in the outer circumference of the first poppet valve and in the middle of the contraction-side pilot passage to operate during a contracting motion. In addition, the poppet valves are driven by a single solenoid. For this reason, a damping force of the hydraulic shock absorber is controlled independently between expanding and contracting motions.